The Internet may be viewed as a collection of Autonomous Systems, where an “Autonomous System” (AS) typically refers to a set of network elements, such as e.g. routers, switches, and controllers, under a single technical administration. The term “network elements” may refer to network elements which could include not only actual physical devices and systems but also devices and systems implemented entirely in software and/or could also include virtual devices and systems components. An AS may also be considered to include hosts connected to the network. Segregation into different AS's allows defining administrative authorities and routing policies of different organizations.
Each AS is “autonomous” (i.e., relatively independent from the other AS's) in a sense that is runs its own independent routing policies and unique Interior Gateway Protocols (IGPs). Exterior routing protocols were created, the current Internet standard EGP being the Border Gateway Protocol (BGP), to exchange routing information between different AS's. For example, the BGP defines an inter-AS routing protocol, where one of the primary functions is to exchange network reachability information (NLRI) using a so-called “BGP speaking system” (also often referred to as a “BGP speaker”).
A BGP speaker typically has the liberty to decide whether it should exchange some NLRIs with certain peers according to a local policy. However, transit control mechanisms that ensure that NLRIs are propagated to certain peers but not others are cumbersome to manually maintain. Therefore, a need exists for an improved transit domain control, in particular an improved BGP transit domain control.